In many industrial processes a process gas containing pollutants is generated. One such industrial process is the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, whereby a hot process gas is generated, often referred to as a flue gas, containing pollutants including acid gases, such as sulphur dioxide, SO2. It is necessary to remove as much of the acid gases as possible from the flue gas before the flue gas may be emitted to the ambient air. Another example of an industrial process in which a process gas containing pollutants is generated is the electrolytic production of aluminium from alumina. In that process, a process gas containing sulphur dioxide, SO2, is generated within venting hoods of the electrolytic cells.
U.S. Pat. No. 5,484,535 discloses a seawater scrubber. In the seawater scrubber seawater taken from the ocean is mixed with flue gas from a boiler. In the seawater scrubber sulphur dioxide, SO2, is absorbed in the seawater and forms sulphite and/or bisulphite ions. Effluent seawater from the seawater scrubber is forwarded to an aeration pond. Air is bubbled through the effluent seawater in the aeration pond for the purpose of oxidizing, by means of oxygen gas contained in the air, sulphite and/or bisulphite ions to sulphate ions that may be released back to the ocean together with the effluent seawater.